Method of repairing shrouded turbine blades with cracks in the vicinity of the outer shroud notch

ABSTRACT

A method of repairing a damaged notch fillet radius of a turbine blade shroud includes a replacement notch fillet radius and a hardface nugget. The damaged notch fillet radius is blended out and a hardface structure positioned proximate the damaged notch fillet radius is removed. A replacement notch fillet radius is formed with weld filler and the hardface nugget is welded to at least a portion of the replacement notch fillet radius.

BACKGROUND OF THE INVENTION

The present invention generally relates to the field of repairingshrouded turbine blades. In particular, the invention relates to amethod of repairing a notch fillet radius of a shrouded turbine blade.

Shrouded turbine blades are often exposed to extreme environments, suchas high temperatures and strong vibrations in aircraft engines. In orderto withstand such environments, shrouded turbine blades are typicallyformed of a nickel-based alloy. Additionally, shrouded turbine bladestypically include a hardface structure within a notch fillet radius thatdissipates the vibrational forces from the surrounding environment.Although the shrouded turbine blade may be wear resistant, the stressesimparted on the shrouded turbine blade and its parts can cause cracks inthe weaker areas of the shrouded turbine blade. For example, the notchfillet radius of the shrouded turbine blade can easily form cracksradiating inward from the edge of the notch fillet radius. If leftunattended, the heat and vibrational stresses of the environment maycause the crack to continue to extend inward and cause the shroudedturbine blade to break.

One problem with repairing a crack located at an outer edge of the notchfillet radius is that the hardface structure is typically formed of abrittle material, such as a cobalt-based alloy. This is in contrast tothe softer nickel-based alloy forming the shrouded turbine blade. Thus,traditional repair techniques are limited to blending techniques toremove the damaged area. Most of these current repair techniques canonly repair the notch fillet radius of the shrouded turbine blade if thecrack is no more than approximately 0.03 inches deep inward from theouter edge of the notch fillet radius. If the depth of the crack isgreater than approximately 0.03 inches, the entire shrouded turbineblade must typically be replaced. This can be a costly process,particularly if there is only a single crack or if only a smallpercentage of the shrouded turbine blade is damaged. Therefore, it wouldbe desirable to have methods that allow cracks greater thanapproximately 0.03 inches deep in the notch fillet radius of shroudedturbine blades to be repaired so that more parts could be salvaged.

BRIEF SUMMARY OF THE INVENTION

Methods of repairing a damaged notch fillet radius of a turbine bladeshroud are described. The damaged notch fillet radius is blended out anda hardface structure positioned proximate the damaged notch filletradius is removed. A replacement notch fillet radius is formed with weldfiller and a hardface nugget is welded to at least a portion of thereplacement notch fillet radius. Conventional techniques are then usedto return the blade to serviceable condition. These methods allow cracksup to approximately 0.1 inches deep to be repaired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a turbine blade.

FIG. 2 is an enlarged top view of a shroud of the turbine blade.

FIG. 3 is an enlarged view of a crack located at a notch fillet radiusof the turbine blade.

FIG. 4 is an enlarged view of the notch fillet radius with the crackremoved.

FIG. 5 is an enlarged view of the notch fillet radius with a hardfacestructure of the turbine blade removed.

FIG. 6 is an enlarged view of the notch fillet radius with a replacementweld.

FIG. 7 is an enlarged view of the notch fillet radius with thereplacement weld shaped to accept a hardface nugget.

FIG. 8 is an enlarged view of the notch fillet radius with the hardfacenugget.

FIG. 9 is a block diagram of a method of repairing a damage site of anotch fillet radius of a turbine blade.

DETAILED DESCRIPTION

The new methods of repairing damaged shrouds of turbine blades describedherein allow cracks having a depth of up to approximately 0.1 inches tobe repaired. The cracks are located at a notch fillet radius of theshroud, radiating inward from an outer edge of the shroud. The crack andthe damaged area around the crack are first blended out locally. Ahardface structure of the shroud is then either machined or ground off.A replacement weld is then formed at the notch fillet radius where thecrack was removed. After the replacement weld is formed on the shroud,the surface is prepared to accept a hardface nugget. The hardface nuggetis then welded to the shroud and the replacement weld at the samelocation where the hardface structure was located. Conventional methodsare then used to place the turbine blade in serviceable condition.

FIGS. 1 and 2 show a perspective view of turbine blade 10 and a top viewof shroud 12 of turbine blade 10, respectively, and will be discussed inconjunction with one another. Turbine blade 10 generally includes shroud12 positioned at a top end 14 of turbine blade 10. Shroud 12 has anoriginal edge 16 and generally includes air seals 18, notch filletradius 20, and hardface structures 22. Notch fillet radius 20 is formedat original edge 16 of shroud 12. Hardface structure 22 is welded tooriginal edge 16 adjacent notch fillet radius 20 and functions todissipate the vibration energy when hardface structure 22 rubs againstadjacent blade hardfaces. In operation, the shrouds of adjacent turbineblades are positioned next to each other such that each notch filletradius 20 of shroud 12 abuts a hardface structure of an adjacent shroudon either side of shroud 12. Turbine blade 10 is exposed to hightemperatures and vibratory stresses present in jet turbine engines withloads constantly exerted on original edge 16 of shroud 12, andparticularly notch fillet radius 20. Thus, notch fillet radius 20 andthe area proximate notch fillet radius 20 can crack, with the cracktypically radiating inward. Whereas current repair techniques only allowcracks of up to approximately 0.03 inches deep to be repaired, the newmethods of repairing cracks described herein allow cracks up toapproximately 0.1 inches deep to be repaired. This allows many parts tobe repaired instead of being scrapped.

FIG. 3 shows an enlarged view of original edge 16, notch fillet radius20, and hardface structure 22 of shroud 12. Original edge 16 forms theouter perimeter of shroud 12. Notch fillet radius 20 has crack 24radiating from original edge 16 of shroud 12. Crack 24 is caused by thehigh temperature and vibration stressed environment in which shroud 12is located. Crack 24 has a height of depth D_(a) and a width of depthD_(b). When depth D_(a) of crack reaches approximately 0.03 inches asmeasured from edge 16, shroud 12 can no longer be adequately repaired byconventional blending, or grinding, methods. Cracks with depth D_(a) ofup to approximately 0.1 inches can be repaired using the followingrepair method.

FIG. 4 shows an enlarged view of original edge 16 and hardface structure22 after crack 24 (shown in FIG. 3) has been removed from shroud 12. Inorder to repair shroud 12 back to serviceable condition, crack 24 mustbe completely removed from shroud 12. Crack 24 and the area proximatecrack 24 to a height of at least depth D_(a) and a width of at leastdepth D_(b) are thus blended out such that notch fillet radius 20 (shownin FIG. 3) is substantially removed from shroud 12. A portion oforiginal edge 16 is removed from shroud 12 proximate notch fillet radius20, forming new edge 16 a at notch fillet radius 20. Crack 24 and thearea proximate crack 24 may be removed by blending, grinding, machining,or any other method known in the art. Original edge 16 may be blendedout from shroud 12 either normally with respect to a plane of shroud 12or at an angle with respect to shroud 12 in order to create a greatersurface area to which replacement parts may be welded.

FIG. 5 shows an enlarged view of new edge 16 a after notch fillet radius20 and hardface structure 22 have been removed from shroud 12. Aftercrack 24 (shown in FIG. 3) and the area proximate crack 24 have beenblended out from shroud 12, hardface structure 22 (shown in FIG. 4) isalso removed from shroud 12. Hardface structure 22 may be removed in anysuitable manner, such as by machining or grinding hardface structure 22from shroud 22. Removal of crack 24, the area proximate crack 24, andhardface structure 22 essentially entirely eliminates original edge 16(shown in FIG. 3) and forms new edge 16 a as the new perimeter of shroud12.

FIG. 6 shows an enlarged view of new edge 16 a and notch fillet radius20 with replacement weld 26. Once crack 24 and hardface structure 22(shown in FIG. 3) have been removed from shroud 12, replacement weld 26is formed with a weld filler along a portion of new edge 16 a.Replacement weld 26 is formed to fill in the notch fillet radius removedby blending out crack 24 and has a height of at least depth D_(a) and awidth of at least depth D_(b). Replacement weld 26 thus takes the shapeof notch fillet radius 20 that was previously removed and extends newreplacement weld edge 16 b back to at least original edge 16 at notchfillet radius 20. While any suitable weld filler material may be used,in one embodiment, a suitable weld filler is a nickel-based alloy knownas Inconel 625, available from International Nickel, Inc., Saddle Brook,N.J.

FIG. 7 shows an enlarged view of original edge 16, new replacement weldedge 16 b, and notch fillet radius 20 with an edge portion 28 ofreplacement weld 26 shaped to accept a hardface nugget 30 (shown in FIG.8). Prior to welding hardface nugget 30 onto shroud 12, edge portion 28of replacement weld 26 must be shaped to accept hardface nugget 30.Because hardface structure 22 (shown in FIG. 4) had a height of depthD_(c) and a width of depth D_(d), edge portion 28 or replacement weld 26and new replacement weld edge 16 b must be shaped to a height of atleast depth D_(c) and a width of at least depth D_(d) from new edge 16 ato properly prepare edge portion 28 and new edge 16 a to accept hardfacenugget 30. Edge portion 28 of replacement weld 26 may be properly shapedto accept hardface nugget 30 by machining or any other suitable manner.

FIG. 8 shows an enlarged view of new replacement weld edge 16 b, newhardface nugget edge 16 c, and notch fillet radius 20 with hardfacenugget 30 welded to shroud 12 and replacement weld 26. Hardface nugget30 has substantially the same shape as hardface structure 22 (shown inFIG. 3) with a height of at least depth D_(c) and a width of at leastdepth D_(d). Hardface nugget 30 is welded onto shroud 12 at new edge 16a and shaped edge portion 28 of replacement weld 26. Welding hardfacenugget 30 to shroud 12 extends the remaining portion of new hardfacenugget edge 16 c back to at least original edge 16. In one embodiment,hardface nugget 30 is welded to shroud 12 by gas tungsten welding atbetween approximately 10 amps and approximately 25 amps, but anysuitable welding technique may be used. After hardface nugget 30 hasbeen welded onto shroud 12, conventional notch repair procedures may beused to restore hardface nugget 30 and surrounding areas (i.e.,replacement weld 26) to serviceable condition. Examples of suitableconventional notch repair procedures include, but are not limited to:grinding, degreasing, stress-relieving, and shot peening.

FIG. 9 shows a block diagram of an exemplary, non-limiting method 100 ofrepairing shroud 12 with crack 24 located at notch fillet radius 20.Conventional blending techniques can repair cracks only up to a depth ofapproximately 0.03 inches. Method 100 allows the repair of cracks havinga depth of up to approximately 0.1 inches. Conventional blendingtechniques can repair cracks only up to a depth of approximately 0.03inches. As shown in Box 102, crack 24 and the surrounding damaged areaof notch fillet radius 20 are blended out locally. Hardface structure 22is then either machined or ground off of shroud 12, as represented byBox 104. As described in Box 106, replacement weld 26 is formed at newedge 16 a and notch fillet radius 20 with a weld filler to fill in thearea previously removed in Box 102. After replacement weld 26 has beenformed on shroud 12, shroud 12 is prepared to accept hardface nugget 30by machining edge portion 28 of replacement weld 26, as represented byBox 108. Hardface nugget 30 is welded to shroud 12 and replacement weld26 at the same location that hardface structure 22 was located, asrepresented by Box 110. As depicted in Box 112, after hardface nugget 30has been welded onto shroud 12, shroud 12 is restored to serviceablecondition using conventional notch repair procedures, which can include,for example: grinding, degreasing, stress-relieving, shot peening, andthe like.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A method of repairing a damaged notch fillet radius of a turbineblade shroud, the method comprising: blending out the damaged notchfillet radius; removing a hardface structure positioned proximate thedamaged notch fillet radius; forming a replacement notch fillet radiuswith weld filler; and welding a hardface nugget to at least a portion ofthe replacement notch fillet radius.
 2. The method of claim 1, whereinwelding the hardface nugget comprises gas tungsten arc welding.
 3. Themethod of claim 1, wherein welding the hardface nugget comprises weldingat a power of between about 10 amps and about 25 amps.
 4. The method ofclaim 1, wherein forming a replacement notch fillet radius with weldfiller comprises using a nickel-based alloy.
 5. The method of claim 4,wherein the nickel-based alloy comprises Inconel-625.
 6. The method ofclaim 1, further comprising: preparing the replacement notch filletradius for the hardface nugget prior to the welding step.
 7. The methodof claim 6, wherein preparing the replacement notch fillet radius for ahardface nugget comprises shaping the replacement notch fillet radius toaccept the hardface nugget.
 8. A method of repairing a crack located atan outer notch fillet radius of a turbine blade shroud, the methodcomprising: removing a portion of the outer notch fillet radius and ahardface structure of the outer notch fillet radius proximate the crack;forming a replacement weld at the outer notch fillet radius with afiller material; shaping the replacement weld for accepting a hardfaceweld; and welding the hardface nugget to at least a portion of thereplacement weld.
 9. The method of claim 8, wherein forming thereplacement weld comprises using a nickel-based alloy.
 10. The method ofclaim 9, wherein the nickel-based alloy comprises Inconel-625.
 11. Themethod of claim 8, wherein the crack has a maximum depth of about 0.1inches from an edge of the outer notch fillet radius.
 12. The method ofclaim 8, wherein the crack has a depth greater than about 0.03 inchesfrom an edge of the outer notch fillet radius.
 13. The method of claim8, wherein removing a portion of the outer notch fillet radius creates agroove in an edge of the outer notch fillet radius.
 14. The method ofclaim 13, wherein forming a replacement weld comprises forming thereplacement weld in at least the groove of the outer notch filletradius.
 15. A method of repairing a damaged notch fillet radius of aturbine blade shroud, the method comprising: grinding away an edgeportion of the damaged notch fillet radius, wherein the damaged notchfillet radius is formed of a first material; removing a structurepositioned proximate the damaged notch fillet radius, wherein thestructure is formed of a second material; building a replacement weldextending from the notch fillet radius, wherein the replacement weld isformed of the first material; shaping the replacement weld for acceptinga hardface, wherein the hardface is formed of the second material; andwelding the hardface to at least a portion of the replacement weld. 16.The method of claim 15, wherein the first material is a nickel-basedalloy.
 17. The method of claim 16, wherein the first material is Inconel625.
 18. The method of claim 15, wherein the damaged notch fillet radiushas a depth of up to about 0.1 inches.
 19. The method of claim 15,wherein the damaged notch fillet radius has a depth of greater thanabout 0.03 inches.